Devices, softwares and methods for incorporating burstiness of packet loss metric in QoS based network routing

ABSTRACT

Devices, software, and methods quantify a burstiness quality of the packet loss in the node of a path. The quantified burstiness becomes a metric for determining the Quality of Service (QoS) offered by a node in retransmitting data through a network. Network routing and rerouting decisions are made according to the improved QoS. The burstiness statistic is determined by counting lengths of episodes of sequentially discarded packets at the node. The burstiness statistic is incorporated as a metric with the other metrics of the QoS of the node.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/998,866, filed Nov. 30, 2001, the disclosure of which is hereinincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to the field of routing algorithmsthrough networks, and more specifically to devices, software and methodsof network routing based on Quality of Service that accounts for thenature of packet loss.

2. Description of the Related Art

Networks, such as the internet, are increasingly used for transmittingvoice data and image data. Network transmission is now described in moredetail.

Referring to FIG. 1, a network 120 is shown having nodes A, B, C, D, E,F, G, H, I, J, K, L, M, N, P, Q, R. Between some (but not all) pairingsof these nodes there are communication links. It will be appreciatedthat the links are intimately associated with the nodes they terminatein.

At each one of these nodes there is a network router, or switch, etc. Anexample is described below.

Referring to FIG. 2 a router 210 at node N of FIG. 1 is described.Router 210 has a central Processing Unit (CPU) 220 and a memory 230.Memory 230 is controlled by CPU 220. Memory 230 is also called a queue,and typically has a certain capacity.

Packets arrive at node N from any source, and are stored in memory 230.Then they are retransmitted from memory 230. The packets arrive and arestored in a sequence, but may be retransmitted according to a differentsequence, depending on their priority. Ordinarily the stored packets areretransmitted before the queue becomes full.

Returning to FIG. 1, when a request for a flow of data arrives, itdefines the two endpoints. In the example of FIG. 1, there is a requestto transmit data from a sender S to a receiver V. The two endpoints arenode A (the first receiver for sender S) and node R (the finaltransmitter for receiver V).

As data travels from endpoint sender S to endpoint receiver V, a path isdefined between nodes within the network. The path is along variousnodes of the network. In the example of FIG. 1, a path 150 is definedvia nodes A, E, J, N, R of network 120.

The diagram of FIG. 1 is simplified, in that it shows data flowing onlyone way. In many instances, however, there is also a return path for thedata to flow in the reverse way, such as for two-way telephone and videoconferences. The return path may or may not be the same as path 150.

The so-called routing problem is to decide which nodes the data flowshould be routed through. The routing problem is solved by routingalgorithms. Such algorithms are addressed by a body called the InternetEngineering Task Force (IETF). At the time of the original filing ofthis document with the U.S.A. Patent Office, the IETF maintains awebsite at <www.ietf.org>.

Within the context of IETF, document RFC-2386 points out that routingmay be based on considerations such as Quality-of-Service (QoS). QoS isa set of service requirements that are to be met by the network whiletransporting a data flow. Such service requirements include delay andavailable bandwidth.

Accordingly, QoS-based routing is a routing mechanism under which pathsfor flows are determined based on some knowledge of resourceavailability in the network, as well as the QoS requirement of flows.The resource availability includes metrics also for delay and availablebandwidth.

Present plans to implement QoS based routing intend to account forvarious QoS metrics, for example bandwidth, delay, and packet loss.

Traditionally packet loss is measured in the prior art as simply a rateW, from Equation (1):W=(# of lost packets)/(total # of packets)  Equation (1)

Rate W is determined by counting total numbers of packets, in grossquantities. Then W is imparted in the QoS computation. The higher the W,the lower the computed quality of service (QoS).

Packet loss at a node is now described in more detail. It will beappreciated that packet loss is intimately associated with congestion ata node.

Referring again to FIG. 2, if node N is congested, more packets willarrive than the queue 230 has capacity for. In that case, the additionalpackets are discarded (“lost”, or “dropped”).

Referring now to FIG. 3, a diagram is shown of packets receivedsequentially at the router of FIG. 2. Those stored and retransmitted areshown as clear, while those dropped are shown with an “X” through them.

Losing discarded packets due to network congestion is an expectedoccurrence. There have been successfully implemented backup measures, inat least two main types of situations.

In the first type, protocols that require all packets to be sent have abackup measure for ensuring that each packet has been sent. When apacket is discarded, its loss is traced, and the packet is sent again.This results in duplication of effort, because the packet was routed toa congested node in the first place.

In the second type, real time transmission protocols tolerate losingdiscarded packets. These protocols include applications for Voice overInternet Protocol (“VoIP”) and Video over IP. Packets that are lost willbe replicated by redundancy algorithms, to conceal the lost packets.These only work decreasingly well, as more packets are lost.

Addressing packet loss for QoS only in terms of the W of Equation (1) isinadequate. That is because the computation of Equation (1) makes anassumption that packets will be lost uniformly in time.

That is not true, however. Packet loss is not distributed uniformly intime, but it tends to come in bursts, or groups, which affect perceivedquality of service disproportionately. While the burstiness oruniformity affects the average W of equation (1) only a little, itaffects the network performance more dramatically.

In the first type of situations, it may be less wasteful when wholegroups of packets are retransmitted due to loss, instead of a fewpackets here and there.

In the second type of situations, the resulting quality of thereconstructed image and/or voice will be affected. That is becausepacket loss concealment algorithms work far better when packet loss isuniform than bursty.

BRIEF SUMMARY OF THE INVENTION

The present invention overcomes these problems and limitations of theprior art.

Generally, the present invention provides devices, softwares, andmethods for quantifying a burstiness quality of the packet loss in thenode of a path. The quantified burstiness becomes a metric fordetermining the Quality of Service (QoS) offered by a node inretransmitting data through a network. The burstiness statistic may belengths of episodes of sequentially discarded packets at the node.

Network routing is thus made according to the more insightfullydetermined QoS. Accordingly, the resulting routing yields a consistentquality of service.

The invention will become more readily apparent from the followingDetailed Description, which proceeds with reference to the drawings, inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a network diagram showing a path through a network configuredby a routing algorithm in the prior art for transmitting a data flow.

FIG. 2 is a block diagram of a router in node N of FIG. 1.

FIG. 3 is a diagram of a sequence of packets received at the router ofFIG. 2.

FIG. 4 is a block diagram of a device made according to an embodiment ofthe invention.

FIG. 5 is a flowchart illustrating a method according to an embodimentof the present invention.

FIG. 6 is the network diagram of FIG. 1, further improved according tothe invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

As has been mentioned, the present invention provides devices, software,and methods for quantifying a burstiness quality of packet losses. Theburstiness is also thought of as grouping, or clustering patterns of thelost packets. The burstiness is quantified as a statistic, thenoptionally as a figure of merit, which becomes part of the computedQuality of Service offered by a node in retransmitting data through anetwork. The invention is now described in more detail.

Referring now to FIG. 4, a device 410 made according to an embodiment ofthe invention is described in more detail. Device 410 may be any networkdevice that performs routing, whether it is situated in a network ornot.

Device 410 has a network interface 412 for interfacing with the network.Device 410 also has a processor 414 coupled with network interface 412.Processor 414 may be implemented as a Digital Signal Processor (DSP),Central Processing Unit (CPU), or any other equivalent way known in theart.

Device 410 may additionally include a memory 418, which is also called apacket queue. A program 419 may also reside on memory 418. Functions ofprocessor 414 may be controlled by program 419, as will become apparentfrom the below.

The present invention may be implemented by one or more devices thatinclude logic circuitry. The device performs functions and/or methods asare described in this document. The logic circuitry may include aprocessor that may be programmable for a general purpose, or dedicated,such as microcontroller, a microprocessor, a Digital Signal Processor(DSP), etc. For example, the device may be a digital computer likedevice, such as a general-purpose computer selectively activated orreconfigured by a computer program stored in the computer.

Moreover, the invention additionally provides methods, which aredescribed below. The methods and algorithms presented herein are notnecessarily inherently associated with any particular computer or otherapparatus. Rather, various general-purpose machines may be used withprograms in accordance with the teachings herein, or it may prove moreconvenient to construct more specialized apparatus to perform therequired method steps.

The required structure for a variety of these machines will becomeapparent from this description.

In all cases there should be borne in mind the distinction between themethod of the invention itself and the method of operating a computingmachine. The present invention relates both to methods in general, andalso to steps for operating a computer and for processing electrical orother physical signals to generate other desired physical signals.

The invention additionally provides programs, and methods of operationof the programs. A program is generally defined as a group of stepsleading to a desired result, due to their nature and their sequence. Aprogram made according to an embodiment of the invention is mostadvantageously implemented as a program for a computing machine, such asa general-purpose computer, a special purpose computer, amicroprocessor, etc.

The invention also provides storage media that, individually or incombination with others, have stored thereon instructions of a programmade according to the invention. A storage medium according to theinvention is a computer-readable medium, such as a memory, and is readby the computing machine mentioned above.

The steps or instructions of a program made according to an embodimentof the invention requires physical manipulations of physical quantities.Usually, though not necessarily, these quantities may be transferred,combined, compared, and otherwise manipulated or processed according tothe instructions, and they may also be stored in a computer-readablemedium. These quantities include, for example electrical, magnetic, andelectromagnetic signals, and also states of matter that can be queriedby such signals. It is convenient at times, principally for reasons ofcommon usage, to refer to these quantities as bits, data bits, samples,values, symbols, characters, images, terms, numbers, or the like. Itshould be borne in mind, however, that all of these and similar termsare associated with the appropriate physical quantities, and that theseterms are merely convenient labels applied to these physical quantities,individually or in groups.

This detailed description is presented largely in terms of flowcharts,display images, algorithms, and symbolic representations of operationsof data bits within at least one computer readable medium, such as amemory. An economy is achieved in the present document in that a singleset of flowcharts is used to describe both methods of the invention, andprograms according to the invention. Indeed, such descriptions andrepresentations are the type of convenient labels used by those skilledin programming and/or the data processing arts to effectively convey thesubstance of their work to others skilled in the art. A person skilledin the art of programming may use these descriptions to readily generatespecific instructions for implementing a program according to thepresent invention.

Often, for the sake of convenience only, it is preferred to implementand describe a program as various interconnected distinct softwaremodules or features, individually and collectively also known assoftware and softwares. This is not necessary, however, and there may becases where modules are equivalently aggregated into a single program,with sometimes unclear boundaries. In any event, the software modules orfeatures of the present invention may be implemented by themselves, orin combination with others. Even though it is said that the program maybe stored in a computer-readable medium, it should be clear to a personskilled in the art that it need not be a single memory, or even a singlemachine. Various portions, modules or features of it may reside inseparate memories, or even separate machines. The separate machines maybe connected directly, or through a network, such as a local accessnetwork (LAN), or a global network, such as the Internet.

It will be appreciated that some of these methods may include softwaresteps which may be performed by different modules of an overall parts ofa software architecture. For example, data forwarding in a router may beperformed in a data plane, which consults a local routing table.Collection of performance data may also be performed in a data plane.The performance data may be processed, and accordingly used in a controlplane to update the local routing table, in addition to neighboringones. A person skilled in the art will discern which step is bestperformed in which plane.

In the present case, methods of the invention are implemented by machineoperations. In other words, embodiments of programs of the invention aremade such that they perform methods of the invention that are describedin this document. These may be optionally performed in conjunction withone or more human operators performing some, but not all of them. As perthe above, the users need not be collocated with each other, but eachonly with a machine that houses a portion of the program. Alternately,some of these machines may operate automatically, without users and/orindependently from each other.

Methods of the invention are now described.

Referring now to FIG. 5, a flowchart 500 is used to illustrate a methodaccording to an embodiment of the invention. The method of flowchart 500may also be practiced by device 410, or any other device or combinationof devices that perform routing.

According to a box 510, data packets are received in a first node of anetwork for retransmission. The received data packets are receivedsequentially, and can be from any source.

According to an optional next box 520, some of the received packets arestored in a queue. Alternately, it may be in more than one queue.

According to an optional next box 530, at least some of the receivedpackets are retransmitted from the queue.

According to a next box 540, some of the received packets are discardedwhen the queue is full. These packets are typically discarded beforethey are stored in the queue. Other times, some of the received packetsare discarded merely when the queue has filled up to a preset threshold.If more than one queue is used, they may have different thresholds.

According to a next box 550, lengths are determined of respectiveepisodes of sequentially lost packets. This may be accomplished in anumber of ways. In one case, the length is merely counted as the numberof packets.

In another embodiment, the loss length statistic may be computed by themathematical model known as Markov two-state chain. In this case, “bad”states are defined for all the dropped packets, and “good” states aredefined for all the other received packets. Then it is determined whenthere are transitions in the sequentially received packets between thegood states and the bad states. Then the transitions are counted. Inthat case, the lengths of box 550 may be determined from the numbers ofthe transitions.

According to another box 560, a loss length statistic is determined forthe first node. In some embodiments, the loss length statistic isdetermined from at least the lengths determined in box 550.

The loss length statistic may be any such useful statistic. As anexample, it may be an average duration of episodes of contiguously lostpackets, a variance of such a duration, a maximum such duration, etc. Inaddition, using more than one statistic will yield more accurateresults.

The loss length statistic may alternately be determined from a tablelookup, using at least one collateral parameter. One such collateralparameter may be a residual bandwidth.

In the event that transitions are being counted as per the Markovtwo-state chain, the loss length statistic may be determined fromnumbers of transitions between the good states and the bad states. Itshould be noted that other statistics may also be computed from thesenumbers of transitions, such as averages, etc.

According to a next box 570, the loss length statistic is incorporatedin a routing table. This can be a local routing table. Subsequentrouting will therefore be improved because the resulting routing tablewill include a QoS metric for the burstiness of packet loss.

The above is an example of just one node. This can be generalized to allthe nodes of a path. In such a case, respective loss length statisticsmay be determined for each of the other path nodes. In addition, acombined figure of merit is computed from the determined loss lengthstatistics for all the nodes of the first path.

Accordingly, a combined burstiness statistic (‘q-path’) for the entirepath may be a function of the individual burstiness of the nodes (orinterfaces) A, E, J, N, R. That would be as follows:q-path(150)=f(q-int[A],q-int[E],q-int[J],q-int[N],q-int[R])  Equation(2)

Moreover, combined burstiness statistics of different paths may becompared to each other. The path chosen would have the optimumburstiness statistic. Or they may be compared to a preset minimum. Thepath chosen could be the first one that meets the preset minimum, or theone that exceeds it by the least amount (to conserve bandwidth).

Furthermore, a combined burstiness statistic may be computed for otherpaths. For each, a total QoS is derived. The QoS of different paths maybe compared, and the optimum selected. Or the first path whose QoS thatis found to exceed a preset minimum may be chosen. Alternately, the pathmay be chosen whose QoS exceed the preset minimum by the least amount,to conserve bandwidth.

As an example only, a link state protocol can be used with theq-int[(node)] parameters for the above.

Referring now to FIG. 6, a network 614 is shown. It will be recognizedthat network 614 is the same as the network 120 of FIG. 1, as resultingafter the introduction of device 410 of FIG. 4. Device 410 may besituated anywhere in network 614, including in one of its nodes.

A different routing can be seen in network 614, through path 650. Path650 goes through nodes A, E, G, H, Q, R. After node E, the QoS gradescomputed according to the invention result in routing through node G,instead. This way, congested node N is avoided. Accordingly, the userenjoys a better QoS, even though the new path 650 may go through morenodes (“hops”) than path 150.

A person skilled in the art will be able to practice the presentinvention in view of the description present in this document, which isto be taken as a whole. Numerous details have been set forth in order toprovide a more thorough understanding of the invention. In otherinstances, well-known features have not been described in detail inorder not to obscure unnecessarily the invention.

While the invention has been disclosed in its preferred form, thespecific embodiments as disclosed and illustrated herein are not to beconsidered in a limiting sense. Indeed, it should be readily apparent tothose skilled in the art in view of the present description that theinvention may be modified in numerous ways. The inventor regards thesubject matter of the invention to include all combinations andsubcombinations of the various elements, features, functions and/orproperties disclosed herein.

The following claims define certain combinations and subcombinations,which are regarded as novel and non-obvious. Additional claims for othercombinations and subcombinations of features, functions, elements and/orproperties may be presented in this or a related document.

1. A device comprising: a network interface for coupling to a network;and a processor coupled with the network interface, in which theprocessor is adapted to receive packets in a first node of a network;store some of the received packets in a queue; retransmit some of thestored packets from the queue; discard some of the received packets whenthe queue has filled up to a preset threshold; determine lengths ofrespective pluralities of episodes of sequentially discarded packets;determine a loss length statistic for the first node from at least thedetermined lengths; and incorporate the loss length statistic in arouting table.